Gas tube construction



Aug. 24, I954 J. GIACOLETTO GAS TUBE CONSTRUCTION Filed Oct. 23, 1952 42. .u. a v v 4 a 4 a 2. a a. 2 0 v I. M Q. 0 x .2 w 2 r Wm M Mr? m C N WW. M.

WFMU ORNEI Patented Aug. 24, 1954 GAS TUBE CONSTRUCTIQN Lawrence J.Giacoletto, Princeton, N. J., assignor to Radio Corporation of America,a corporation of Delaware Application October 23, 1952, Serial No.316,425

Claims. 1

This invention relates to electron discharge devices of the type inwhich an ionizable medium is employed to support a discharge. Inparticular, this invention relates to such devices in which a controlelectrode may continuously control or modulate the current through thedevice at a very high rate.

In an article appearing in IRE, volume 40, number 6, June 1952, page645, by Malter, Johnson, and Webster, gas discharge devices aredescribed which can be used in applications in which prior art gas tubeshave been unsatisfactory or could not be used. As is pointed out in theabove identified article, this type of discharge device separates thefunctions of (1) ionizing the tubes ionizable medium and (2) providing apath for the load current through the tube.

The type of tubes with which this invention relates normally includes 1)a group of auxiliary electrodes, comprising an auxiliary cathodesurrounded by an apertured electrode, to provide an auxiliary dischargeand thus ionize the medium; and (2) a group of main electrodescomprising a main thermionic cathode, a control electrode and an anode.Although this general type of discharge device has offered manyadvantages it has, prior to this invention, had certain structurallimitations. One of the structural limitations of this type of dischargedevice has been the requirement of two cathode heaters to heat the twocathodes.

A further structural limitation of this type of discharge device hasbeen that the positive ions formed by the auxiliary discharge are notefliciently nor effectively directed into the main current path. Thisdisadvantage has made necessary the generation of a greater number ofpositive ions.

It is therefore an an object of this invention to provide a new andnovel gas discharge device of the type described that overcomes theabove mentioned disadvantages.

Another object of this invention is to provide a new and novel gasdischarge device of the type described that effectively and efiicientlyutilizes the ions formed by the auxiliary discharge.

A further object of this invention is to provide a new and improved gasdischarge device of the type described that utilizes a single heatingelement to heat both the auxiliary and main cathodes.

A still further object of this invention is to provide a new andimproved gas discharge device of the type described that containscylindrically shaped and concentrically placed elements and thus iseasier to manufacture.

These, and other objects, have been accomplished in accordance with thegeneral aspects of this invention by providing a concentric arrangementof electrodes including a single centrally located heater element. Thesingle heater element is surrounded by a control electrode and an anode.Intermediate the control electrode and the heater element there isprovided an apertured cathode having a coating of thermally heatedelectron emissive material thereon. Immediately surrounding the heaterelement there is an electrode which is in one embodiment an auxiliarycathode, and in another embodiment is an auxiliary anode. The singleheater element heats the electrode which in turn heats, by radiation,the apertured cathode and the desired emission occurs.

These and other features and advantages will best by understood from thefollowing descriptions of the illustrated embodiments when read inconnection with the accompanying drawings wherein like referencecharacters designate similar parts throughout the several views and inwhich:

Figure 1 shows a sectional view in elevation of an embodiment of a gasdischarge device constructed in accordance with this invention;

Figure 2 is a sectional view taken along line 2-2 of Figure 1;

Figure 3 is a sectional View in elevation of a further embodiment of agas discharge device constructed in accordance with this invention; and

Figure 4 is a sectional view taken along line 44 of Figure 3.

Referring now more particularly to Figures 1 and 2, the gas dischargedevice includes an envelope 8 having an ionizable medium therein. Anysuitable gas or mixture of gases may be utilized as the ionizablemedium. The gas pressure for any particular embodiment will be inaccordance with its specific electrode geometry and spacing but is notat all critical and may be varied over wide ranges. A number of tubes ofthe type under consideration have been found to operate satisfactorilywith a filling of helium at a pressure of approximately 750 microns.However, as is well known, other gases and other pressures may be used.

The electrode assembly includes two groups of electrodes, the electrodesfor ionizing the medium, and the electrodes included in the load 01'Work circuit. The group of electrodes for ionizing the medium includesan auxiliary cathode Hl, and the heating element l2. The auxiliarythermionic cathode I is an indirectly heated, oxide coated cathode ofthe conventional type. Surrounding the auxiliary cathode iii are theload circuit group of electrodes. The load circuit group of electrodesincludes an apertured, or perforatedpmain cathode l4;"a controlclestrode l6, and an anode l8 spaced in that order.

All of the electrodes are supported in the envelope in a conventionalmanner by means of support rods l9 and by the two and insulating members29 and 2|. The main apertured, or perforated, cathode is coated'with anyof the Well known thermally activated electron emissive materials 22.The emissive material may be coated on apertured main cathode by-any ofthe well known means, such as spraying and it may be coated on bothsides or only on the side adjacent the control electrode [5. The entireelectrode structure and theend insulating members 20 and 21 aresupportedbythe re-entrant stem, as shown, and are energized in aconventional manner.

In operation of the device, the single heater l2 will supply asufiicient amount of thermal energy both to the auxiliary cathode l2,and to the apertured main cathode i ito heat the electron emissivematerials to cause electron emission. The heat is transferred byradiation between the two cathodes. A potential is applied to theauxiliary cathode K! that is negative with respect to the apertured maincathode l4. The difierence in potential existing between auxiliarycathode IG and apertured main cathode-Iii is greater than the ionizationpotential and may be approximately 100 volts. Due to this difference-inpotential, the electrons emitted by-the auxiliary cathode ii) areattracted to the apertured main cathode l4 and ionize the medium as theyprogress from the auxiliary cathode-l0 to the apertured main cathode [4.These ions-diffuse outward through the apertures of main cathode I4 andform a plasma for themain discharge'between the main cathodeM-andtheanodelt; The difference of potential between the aperturedmaincathode M and the main anode l8, i. e. the main current electrodes,is normally less than the ionization potential of the medium'and may beapproximately 20 volts; Control electrode [6 normally is negative withrespect to anode l3 and may have a signal'applie'dthereto; Controlelectrode 16 controls ithe'main. current in a manner as is more fullyexplained inthe aforementioned article.

Referring nowto Figures 3 and 4, there is shown a gas discharge devicecomprising a sealed envelope 9 having an ionizable medium therein. Theelectrode structure'includes a concentric array of a heater element 28;an auxiliary anode 26, an apertured 0r perforated cathode 39, a controlelectrode 32;and ani'anode 34 arranged in that order with the heaterelement 28 being centrally located. The electrodes are supportedby'support rods 35 and end insulating members 37 and 39' as described inconnection with Figures 1 and 2.

The apertured, or perforated, cathode 3!) is coated on both sides witlrathermally activated electron emissive material-3|: Any ofthe well knownelectron emissive coatings will be suitable as will be any ofthe-conventional methods of applying the electron emissive coating. Theside of the apertured cathodetc adjacent auxiliary anode 26 acts as anauxiliary cathode, and the emissive material is thermally activated bymeans of the radiant heat energy from the heater element 28. The side ofapertured cathode 30 adjacent control electrode 32, since it is alsocoated with electron emissive material, will also act as a cathode butthis side of the apertured cathode 353 will function as a main cathodefor the main group of electrodes. The control electrode 32 and mainanode 34 are similar to those described in connection with Figures 1 and2, so that further description is not deemed necessary.

In operation of the embodiment of the invention shown in Figures 3 and4, auxiliary anode 26 is heated by means of the heater element 28. Theauxiliary anode 2B is also electrically energized so that it is positivewith respect to apertured cathode30 by means of the connection throughresistor All to source 36. When desired resistor ill may be connected toa tap on source 36. The apertured cathode 38 may be at ground potential,as shown, if desired. As in conventional structures, main anode S llspositive with respect to apertured cathode so by being connected throughload 38 tosource 35, and a signal may be applied to control electrode 32as shown. It

should be noted that the device is completely connected while using onlya single source 36. The heater elements 23 may also be connected to thissource if desired by conventional taps on the source 38.

The heat from heating element 23 heats the auxiliary anode 25 which inturn radiates heat to apertured cathode 39 so that the electron emissivematerial is heated. Thus electron emission occurs from both sides of theapertured cathode St. the apertured cathode are attracted toward theauxiliary anode 2E and will cause ionization in this region. Thepositive ions that are formed by this ionization are repelled from theauxiliary anode 2t and travel out through the apertured cathode 3! intothe main current path and thus form a plasma in this region. Theelectrons from the outside or apertured cathode 38 are, because of theattraction of main anode 3t, attracted toward the main anode 3t and maybe modulated as explained in the above identified co-pendingapplication.

This invention should not be limited to the method of connecting thevarious elements that are shown in Figure 4 for this diagram i givenmerely to show a method of connecting the tube so that only one powersupply is required. It

should be understood that conventional circuits may also be utilized.

I claim:

1. A gas-discharge device, comprising a sealed envelope having anionizable medium therein, a heater element, an array of electrodesincluding an electrode, an apertured indirectly heated thermioniccathode, a control electrode and an anode spaced in that order from saidheater element and within said envelope.

2. A gas discharge device, comprisin a sealed envelope having anionizable medium therein, a single heater element, an array ofelectrodes including an electrode for afiecting charged particles ofsaid medium, an apertured indirectly heated thermionic cathode, acontrol electrode and an anode spaced in that order from said heaterelement and within said envelope.

3. A gas discharge device, comprising a sealed envelope having anionizable medium therein, a single heater element, a concentric array ofelectrodes including an electrode for afiecting charged The electronsemitted from the inside of particles of said medium, an aperturedindirectly heated thermionic cathode, a control electrode and an anodespaced in that order around said heater element and within saidenvelope.

4. A gas discharge device, comprising a sealed envelope having anionizable medium therein, a single heater element, an array ofelectrodes including an electrode for afiecting charged particles ofsaid medium, an apertured indirectly heated thermionic cathode, acontrol electrode and an anode spaced in that order within saidenvelope, said single heater element being centrally located.

5. A gas discharge device, comprising a sealed envelope having anionizable medium therein, a heater element within said envelope, ahollow anode surrounding said heater element but spaced therefrom andwithin said envelope, 2. control electrode surrounding said heaterelement and spaced intermediate said anode and said heater element, anapertured cathode surrounding said heater element and spacedintermediate said control electrode and said heater element, saidapertured cathode having a coating of electron emissive materialthereon, and a hollow electrode for affecting charged particles of saidmedium spaced around said heater element and intermediate said heaterelement and said apertured cathode.

6. A gas discharge device, comprising a sealed envelope having anionizable medium therein, a heater element within said envelope, ahollow tubular shaped anode coaxially spaced around said heater element,a hollow tubular shaped control electrode coaxially spaced around saidheater element and intermediate said heater element and said anode, ahollow tubular shaped apertured cathode coaxially spaced around saidheater element and intermediate said control electrode and said heaterelement, said apertured cathode having a coating of electron emissivematerial thereon, a hollow tubular shaped electrode for afiectingcharged particles of said medium coaxially spaced around said heaterelement and intermediate said heater element and said perforatedcathode.

7. A gas discharge device, comprising a sealed envelope having anionizable medium therein, a hollow tubular shaped auxiliary anodesurrounding a heater element and within said envelope, a hollow tubularshaped main anode coaxially spaced around said auxiliary anode, acontrol electil trade coaxially spaced around said auxiliary anode andintermediate said auxiliary anode and said main anode, a hollow tubularshaped perforated cathode coaxially spaced around said auxiliary anodeand intermediate said auxiliary anode and said control electrode, andsaid perforated cathode having a coating 0t electron emissive materialon both sides.

8. A gas discharge device, comprising a sealed envelope having anionizable medium therein, a hollow tubular shaped indirectly heatedauxiliary thermionic cathode surrounding a heater element and withinsaid envelope, a hollow tubular shaped anode coaxially spaced aroundsaid auxiliary cathode, a tubular shaped control electrode spacedcoaxially around said auxiliary cathode and intermediate said auxiliarycathode and said anode, an apertured main cathode coaxially spacedaround said auxiliary cathode and intermediate said auxiliary cathodeand said control electrode, and said main cathode having a coating ofelec tron emissive material on the side adjacent said control electrode.

9. A gas discharge device comprising, a sealed envelope having anionizable medium therein, a heater element, an array of electrodesincluding an auxiliary anode, an apertured indirectly heated thermioniccathode, a control electrode and a main anode spaced in that order fromsaid heater element and within said envelope.

10. A gas discharge device comprising, a sealed envelope having anionizable medium therein, a heater element, an array of electrodesconcentrically spaced around said heater element and including anauxiliary anode, an apertured indirectly heated thermionic cathodehaving an electron emissive coating thereon, a control electrode and amain anode spaced in that order around said heater element and withinsaid envelope.

References Cited in the file of this patent UNITED STATES PATENTS

